The present invention relates generally to a discharge lamp, more specifically to a dielectric barrier discharge lamp for radiating light (ultraviolet or UV) by high frequency excitement and electrically discharging of inert gas such as nitrogen sealed in a tube.
Discharge lamps to radiate strong ultraviolet are used in exposure systems for fabrication of various electronic devices such as semiconductor integrated circuits (ICs), liquid crystal display devices, printed circuit boards, etc. One example of such discharge lamps is dielectric barrier excimer discharge lamp. Conventional dielectric barrier excimer discharge lamps are disclosed in JP-A-7-14553 and JP-A-6-310104 entitled xe2x80x9cDielectric Barrier Discharge Lampxe2x80x9d. Such conventional dielectric barrier discharge lamps comprise a discharge tube (envelope) including an inner tube and an outer tube, internal and external electrodes, a getter, a discharge space and a protrusion.
Cooling material such as cooling water flows inside the inner tube to prevent the discharge tube from being overheated by the heat generated by electrical discharge of such dielectric barrier discharge lamp. Preferably, such dielectric barrier discharge lamps have stable UV radiation over a long time and have longer lifetime. For example, degradation in UV radiation efficiency of such dielectric barrier discharge lamps requires longer exposure time and decreases fabrication efficiency of such electronic devices and thus increases production cost thereof. Also, shorter lifetime of dielectric barrier discharge lamps increases cost of fabrication facilities and thus devices fabricated thereby.
Such dielectric barrier discharge lamps have potential problems to decrease light transparency by dust or other foreign material collected on the surface of the discharge tube or envelope or impurities in the discharge gas sealed in the discharge tube. As a result, there is a need to clean or replace the discharge tube, which is not easy to perform. Additionally, conventional dielectric barrier excimer discharge lamps are insufficient in mechanical strength.
It is therefore an object of the present invention to provide a dielectric barrier discharge lamp that is simple in construction and easy to disassemble or replace the discharge tube. The dielectric barrier discharge lamp according to the present invention is a lamp having coaxial inner and outer tubes filled with inert gas in the space between the inner and outer tubes and internal and external electrodes to which excitation voltage is applied. The dielectric barrier discharge lamp features in the internal electrode comprising an electrically conductive rod inserted into a center hole of the discharge tube. The electrically conductive rod is longer than the discharge tube integrally and strongly held in position using a pair of holders.
In a preferred embodiment of the dielectric barrier discharge lamp according to the present invention the pair of holders are removably mounted on both ends of the internal electrode by mounting screws. A light transparent protection tube is mounted outside the discharge tube and the holders by way of pressure rings. The protection tube is sealed with respect to the holders to fill refrigerant such as inert gas in the space between the protection tube and the holders. The holders have inner and outer diameters substantially equal to those of the discharge tube. A space to flow cooling water or the like is formed between the outer surface of the internal electrode and the inner surfaces of the holders and the discharge lamp.